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ABSTRACT:A new type of hydrogel, transparent cellulose hydrogel (TCG), is the aqueous dispersion of cellulose nanofibers (microfibrils) 10 nm in width and several hundreds nanometers in extended fiber length, and shows unique rheological properties leading to unique applications. The rheological properties of TCG, especially their dependences on temperature were investigated through the spin-spin relaxation time (T 2 ) analysis in 1 H NMR for water in the systems. Viscosity under low shear stress and T 2 of water (being very short for T 2 value) were proved to be constant in a wide range of temperature (ca. 30-80 C). These results may be explained by two considerations that network in TCG gradually grows with increasing temperature but collapses by adding weak shear stress and that TCG gel has large amount of bound water. It was also confirmed that the ionic strength such as pH and NaCl concentration sensitively influences on rheological parameters. With increasing ionic strength, the network formation and the successive aggregation of microfibrils occur and both should be interpreted in terms of the electrostatic interaction between negative charge on a cellulose surface and cationic aqueous layer around it (i.e., electric double layer). [DOI 10.1295/polymj.36.684] KEY WORDS Cellulose / Hydrogel / Nanofiber / Microfibril / Rheology / Spin-Spin Relaxation Time / Network / We have already found a preparation method of a new type of hydrogel, transparent cellulose hydrogel (TCG, Figure 1a), an aqueous dispersion of cellulose microfibrils (degree of polymerization: ca. 40) having low crystallinity with about 10-15 nm in diameter and several hundred nanometers in extended length ( Figure 1b) and reported the results for its characterization and properties. 1,2 This new nanomaterial was prepared by downsizing by chemical (hydrolysis reaction) 3 and mechanical (smashing by a ultra high pressure homogenizer) techniques. Resultant cellulose microfibrils in TCG are flexible fibrous particles, i.e., ''nanofibers'', having nano-size diameter (Figure 1b) and show strong attractive interaction based on hydrogen bonding between hydroxyl groups localized densely on their surfaces, leading to quite unique rheological properties. In view of the application, four major unique properties of TCG are pointed out 2 as follows: 1) Rheological properties such as very high viscosity under the low share stress, a large thixotropic character and low fluctuation of rheological parameters in the range of ambient temperature to the higher temperature region, 2) Formation of transparent coating film on substrate materials by drying, 3) Formation of cellulose microspheres having average particle size of less than 5 mm by spray drying, and 4) Stabilizing ability as an additive for aqueous suspension systems such as aqueous dispersion of inorganic particles (SiO 2 , TiO 2 , . . ., etc.) and O/W type emulsion (also as an emulsifier).Especially from an industrially applicable aspect, we discovered that TCG is a gel which can be sprayed by only ...

Section: A) B)supporting

confidence: 58%

Section: A) B)mentioning

confidence: 96%

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1H Spin–Spin Relaxation Time of Water and Rheological Properties of Cellulose Nanofiber Dispersion, Transparent Cellulose Hydrogel (TCG)

Ono

Shimaya

Sato

et al. 2004

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“…2 Such apparent concentration-specific structural change in cellulose is also observed in measurements of 1 H spin-lattice relaxation of cellulose for a cellulose-water system as a function of concentration of water. 3 Molecular mobility of cellulose increases and reaches a maximum around 30 wt % of water content, at which the water works as a thermo-plasticity agent on the cellulose in the system. 2,3 On the one hand, it has been also shown that hydrophobic solvents affect the morphology and structure of cellulose: G. N. Marchenko et al 4 reported on wood pulp and cotton that dichloromethane (DCM) facilitated an intra-fibril swelling and gave some changes in a absorption of CH 2 -vibration (IR; 1380 cm À1 ) with no practical change in X-ray crystallinity.…”

mentioning

confidence: 99%

Effect of Solvent on Morphological and Structural Change of Cellulose under Ball-Milling

Ago

Endo

Okajima

2007

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ABSTRACT:Cellulose derived from cotton was ball-milled with some hydrophilic and hydrophobic solvents such as water, toluene, 1-butanol and also without solvent (dry state), and effect of the solvents on morphological and structural changes of the cellulose were investigated. The original fibrous cellulose was changed to the aggregated globular particles by water and dry state ball-milling, plate-like particles by toluene processing, and a mixture of rugged globular particles and plate-like particles by 1-butanol processing. The globular particles prepared without solvent showed fairly low crystallinity and their inter-and intra-molecular hydrogen bonds were deformed, leading to an increase in free hydroxyl groups. The globular particles prepared with water exhibited a mixture of crystalline structure as cellulose I, cellulose II and non-crystalline state. In the case of the products with toluene, the plate-like particles significantly retained their original crystalline structure and hydrogen bonds. The 1-butanol processing seems to give the particles consisting of cellulose I and small amounts of either non-crystalline or cellulose II. The cellulose/dye stuff mixtures under the presence of the above solvents were prepared using 4-aminoazobenzene to investigate the differences in the surface property of the particles prepared by the ball-milling processing. Characteristic color development of each cellulose particles was clearly distinguished depending on the effect of the solvent (cinnabar; without solvent, yellow; toluene and yellowish-green; water or 1-butanol It has been shown that a typical hydrophilic solvent, water causes change in the long-periodicity of regenerated cellulose fiber at 30-40% water content 1 and the amorphous cellulose prepared by a ball-milling treatment reorganizes effectively to cellulose II crystalline by ball-milling with a specific amount of water; 30 wt %.2 Such apparent concentration-specific structural change in cellulose is also observed in measurements of 1 H spin-lattice relaxation of cellulose for a cellulose-water system as a function of concentration of water.3 Molecular mobility of cellulose increases and reaches a maximum around 30 wt % of water content, at which the water works as a thermo-plasticity agent on the cellulose in the system. 2,3On the one hand, it has been also shown that hydrophobic solvents affect the morphology and structure of cellulose: G. N. Marchenko et al. 4 reported on wood pulp and cotton that dichloromethane (DCM) facilitated an intra-fibril swelling and gave some changes in a absorption of CH 2 -vibration (IR; 1380 cm À1 ) with no practical change in X-ray crystallinity. A concentration-specific interaction of toluene with a regenerated cellulose membrane with high planar orientation has been proved to show that the orientation of (1 1 10) plane in cellulose crystal preferentially lowers around 20-40 wt % of toluene content, elucidated by X-ray diffraction patterns. 5 These observations show that cellulose molecules can transform spontaneously i...

“…2 Ago et al also showed that amorphous cellulose is reorganized to cellulose II crystals by ball-milling preferentially when water content is ca. 30%.…”

mentioning

confidence: 99%

Effects of Hydrophobic Solvents on X-Ray Diffraction Patterns of Regenerated Cellulose Membrane

Sato

Mochizuki

Okajima

et al. 2004

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ABSTRACT:Specific interactions between cellulose and hydrophobic solvents were studied using highly planar oriented cellophane and X-Ray diffraction analysis. The planar orientation index ( f kð1 1 10Þ ) was found to decrease considerably by hydrophobic solvent treatment. Toluene, a hydrophobic solvent, caused decrease at specific concentration in f kð1 1 10Þ at toluene content of ca. 20-40 wt % to cellulose with keeping its crystallinity and the degree of intermolecular hydrogen bonding. The molecular sheet-like assembly (corresponding to sh relaxation), proposed previously by Yamane et al. [Polym. J., 28, 1039(1996] may be a plausible explanation of the result. Analysis of X-Ray diffraction intensity of cellulose/solvent systems might give some information on the extent of interaction between cellulose and solvent in question. However, whether such change in specific solvent concentration with orientation index is related to the long-periodicity change, as observed for water, should be studied. [DOI 10.1295/polymj.36.478] KEY WORDS Cellulose / Planar Orientation / Hydrophobic Solvent / X-Ray Diffraction / Crystal Plane / Molecular Sheet / Water causes a sudden long-periodicity change of regenerated cellulose fiber at ca. 30 wt %.1 Such concentration-specific structural change for natural cellulose was also observed indirectly by T 1 measurement of water in cellulose.2 Ago et al. also showed that amorphous cellulose is reorganized to cellulose II crystals by ball-milling preferentially when water content is ca. 30%.3 Hydrophobic solvents such as hexane, toluene and dichloromethane are captured in cellulose domain even after some severe vacuum drying.4 Such nonpolar solvents have been frequently utilized as heterogeneous reaction media for converting cellulose to its derivatives. Marchenko et al.5 studied structural changes in cellulose (wood pulp, cotton) caused by dichloromethane (DCM) by using X-Ray diffraction, IR, and SEM analyses, and noted intrafibrillar swelling, no practical change in X-Ray crystallinity, some changes in CH 2 vibration (IR; 1380 cm À1 ) absorption, a loosening of cellulose structure by penetration of DCM into nonordered region and formation of rigid cellulose structure after removal of DCM. Such studies are quite important, although not much research seems to have been done. Recently, we have reported the mechanical molecular alloy preparation of cellulose/thermoplastics in the presence of such a nonpolar solvent.6,7 The method is based on the facts that 1) such solvents lowers the temperature (a kind of T g ) considerably, representing sh relaxation mode (inner phase relaxation of cellulose main chains on molecular sheet-like assembly 8,9on tan -T curves, from ca. 170 C to less than room temperature 9 and 2) such solvents might induce concentration-specific mobilization of cellulose chains. Therefore, more detailed studies on the interaction of cellulose with nonpolar solvents are immediately required. Recently, a concentration-specific interaction between cellulose with hydrophobic ...